The purpose of this research is to continue an investigation of the means by which a mammalian free muscle graft adapts to its new environment and becomes functionally reintegrated with the host. This phase of the research will concentrate upon three specific problems. The first is the question of viability of cells within the avascular central zone of a muscle graft. This is linked with the problem of the origin of the cells that ultimately form muscle in this region. The second area of emphasis will be the question of muscular neurotization of free muscle grafts. We propose to map out the time course and pattern of innervation of muscle grafts that are being innervated by muscular rather than neural neurotization. Preliminary studies aimed at uncovering the mechanisms of this process will also be under-taken. The third area of emphasis will be the degeneration and regeneration of muscle spindles within free muscle grafts. Emphasis will be placed upon conditions and possible interactions involved in their formation. Most of the experiments will be conducted upon rats. Methods used will include experimental surgery, histology, electron microscopy, autoradiography, histochemistry and contractile physiology.